Methods of cladding stainless steel to aluminum



Nov. 7, 1,967 J. B. ULAM ETAL METHODS OF CLADDING STAINLESS STEL TO ALUMINU Filed Aug. l5, 1962 INVENTORS h B Ul www; c coma L I f l ,f/M

United States Patent 3,350,772 METHODS 0F CLADDING STANLESS STEEL T0 ALUMINUM John B. Ulam and Wiiliam C. Camp, Canonsburg, Pa.,

assignors to Composite Metal Products, Enc., a corporation of Pennsylvania Filed Aug. 15, 1962, Ser. No. 217,036 3 Claims. (Cl. 29-488) This invention relates to methods of cladding metals and particularly to methods of bonding stainless steel to aluminum or other dissimilar metals together. Various methods of cladding metals have been heretofore proposed, however, these methods do have certain limitations and drawbacks. There are instances where it is desirable to have varying degrees of hardness in the two metals which form the composite clad or to control the physical properties of the two metals in the final product. This has been virtually impossible to -accomplish in the methods heretofore proposed.

We have discovered a method of cladding metals which overcomes the ditiiculties of prior art practices and makes it possible to provide close control over the physical properties of the metals. in the ultimate `composite clad metal and at the same time to control and provide a strong bond between the dissimilar metals forming the clad body.

In the `preferred practice of our invention, we clean the surfaces of the metals tobe bonded by a mechanical or chemical procedure that removes all of the oxide from the surface. Preferably, the oxides, dirt, oil, etc., are removed byV mechanical cleaning such as abrasive grinding so as to expose a perfectly clean surface. This practice is described inthe Ulam Patents, 2,718,690 and 2,758,368. After the metals to be joined are cleaned they are heated in separate furnaces to la temperature selected to provide the desired characteristics in the finished metal and `in an atmosphere which protects the metal surfaces from oxidation and the clean surfaces are then brought together within a like protective atmosphere and pressure is applied to cause the metals to be bonded and reduced. Preferably, the heating and bringing together of the clean surfaces is carried out in an inert atmosphere, a reducing atmosphere, or a vacuum.

In the accompanying figure, we have illustrated the practice of our invention as applied to a stainless clad aluminum.

In the figure, a coil of stainless steel 10 and a coil of aluminum 11 are fed on separate strip lines 13 and 14 to abrasive grinding wheels 15 and 16 which clean the two surfaces to be joined. The two strips are immediately carried into two separate heating chambers 17 and 18 which are provided with an inert gaseous atmosphere. In each of these furnaces 17 and 18, the strips of stainless and aluminum, respectively, are heated to temperatures above their stress relieving temperature, which temperatures are considerably different for these two metals. In the case of stainless steel in this example, the minimum temperature would be about 700 F. and the strip could ice be heated as high as 1850 F. where full softening takes place. In the case of aluminum, the temperature would be about 465 F. The two strips are then brought together in a chamber 19 having the same inert atmosphere as the furnace while maintaining a temperature differential between them proportional to the difference of their minimum stress relieving temperatures. The strips are brought together by pinch rolls 20 and are fed into a rolling stand 21 where they are reduced and the bonding is completed.

By this practice, it is possible to heat the two metals to different temperatures, thus making possible fusion bonds, diffusion bonds or a combination of fusion and diffusion bonds. For example, if a cleaned stainless steel strip or sheet is led through furnace 17 which heats the stainless steel above its recrystallization temperature, as described above, and the aluminum is also heated in separate furnace 18 to a temperature `above the recrystallization temperature and the two are rolled, there will result a fusion bond with both the stainless steel and the aluminum in the final clad product being in the fully annealed condition. Thus practice also permits more drastic reductions in the metals and thus stronger bonds. In this example, a 60% reduction in either the aluminum or the stainless above their recrystallization temperature has no effect on their ultimate ductility. A 60% reduction in stainless below its recrystallization temperature would be equivalent to 60% cold work and the resulting product would be useless in a forming operation.

ln another example the stainless is heated above the recrystallization temperature and the aluminum below its recrystallization temperature. This would result in la combination fusion-diffusion bond with the stainless steel in the Vfully annealed condition and the aluminum partially hardened.

Another example would be the case where the stainless is heated to a temperature below the recrystallization temperature but above the minimum stress relieving temperature and t-he aluminum above its -recrystallization temperature. This would result in a diffusion bond with fully annealed aluminum and partially hard stainless.

Still another example would require 'that the stainless be heated above the stress relieving temperature and the aluminum would be held at room temperature. This would result in a diffusion bond with stress relieved or fully annealed stainless steel and partially hardened aluminum.

It is obvious that a double stainless clad aluminum could be obtained by passing a second strip of stainless through a third furnace and Vbringing all three elements together with the aluminum as the core in a housing in an inert atmosphere similar to that described above.

Various degrees of hardness in both of the metals forming the composite can be attained by controlling the furnace temperatures and the nal working of the strips in the formation of the clad metal. The varying physical properties which are thus attained can only be achieved by the practice of the present invention.

Typical mechanical properties that can be attained by the practice of this invention are shown in the accompanying table.

TYPICAL MECHANICAL PROPERTIES i Composite Elon- Yiold Tensile gatioii Gage Strength, Strength, in 2 in., Stainless Temp. Aluminum Temp. p.s.i. p.s.i. percent Steel 1".) F.)

304 975 3003 675 250 14, 300 18, 900 23 304 1,100 3003 875 160 15, 100 21, 100 25 304 3003 90 126 1 NT 71,700 22. 5 304 1,600 3003 775 125 16, 200 21, 200 26 304 1, 250 3003 430 125 1 NT 21, 500 21. 5 304 1, 455 3003 900 120 1 NT 22, 000 20. 5 304 950 1100 475 100 17, 800 73, 600 24 304 1, 700 3003 350 100 18, 750 23, 800 32. 5 304 1, 025 1100 850 100 10, G00 Z2, 100 32. 5 304 1, 325 3003 750 008 19, 100 24, 900 27 2 305 900 3003 700 097 l0, 200 24, 100 21 430 900 3003 250 095 23, 110 37, 570 18 305 1, 650 3003 750 094 10,800 75, 000 26 304 1, 175 3003 575 001 23, 760 34, 000 18 304 1, 500 3003 750 091 24, 350 55, 700 22 304 1, 200 3003 S50 090 21, 300 20, 500 25 304 1, 650 3003 800 077 21, 500 28, 600 30 304 1, G50 3003 850 075 23, 300 31, 400 34. 5 304 1, 330 3003 700 067 1 NT 22, 000 24 304 1, 275 3003 700 006 1 NT 23, 000 2G 304 1, 450 3003 700 052 24, 750 32, 900 27 304 1, 500 3003 750 052 26, 700 31, 400 2 304 1, 325 3003 650 .050 24, 600 32, 750 23. 304 1, 400 1100 S90 .050 18, 210 25, 200 27 304 1, 275 3003 775 046 1 NT 26, 500 23 304 1, 275 3003 775 O43 1 NT 28, 600 23 2 304 1,175 3003 90 04 1 NT 29,100 19 304 900 3003 90 042 1 NT 28, 700 13 1 Not Taken. 2 Double Armor.

In the foregoing specification, we have illustrated certain preferred practices of our invention. It will be understood, however, that this invention may be otherwise practiced within the scope of the following claims.

We claim:

1. A method of forming a composite stainless steel and aluminum metal of at least one strip of each of aluminum and stainless steel comprising the steps of heating the strip of stainless steel above its stress relieving temperature but below its fusion temperature while maintaining the aluminum stress relieving temperatures, immediately bringing the surfaces of the heated stainless steel and the aluminum together and exerting pressure on the metals simultaneously to effect reduction and to form a bond between them.

2. A method of forming a composite stainless steel and aluminum metal of at least one strip of each of aluminum and stainless steel comprising the steps of separately and differentially heating each of the stainless steel and aluminum to a temperature above its own individual recrystallization temperature but below its fusion point and immediately bringing the differentially heated strips together `while maintaining a temperature differential between them proportional to the difference of their minimum stress relieving temperatures and exerting pressure On the metals simultaneously to reduce and bond them.

3. A method of forming a composite stainless steel and aluminum metal of at least one strip of each of aluminum and stainless steel comprising the steps of separately and differentially heating each of the stainless steel and aluminum to a temperature above its own individual recrystallization temperature but below its vfusion point, immediately bringing the differentially vheated strips together while maintaining a temperature differential between them proportional to the difference of their minimum stress relieving temperatures and simultaneously reducing said sheets under pressure to produce at least a jreduction in the aluminum sheet.

References Cited UNITED STATES PATENTS 2,879,587 3/1959 Mushovic et al 29-504 X 2,908,073 10/1959 Dulin A7.9-1962 X 3,078,563 2/1963 Gould et al. 29-497.5 X 3,095,500 6/1963 Jost 29-497.5 X 3,210,840 10/1965 Ulam 29-488 JOHN F. CAMPBELL, Primary Examiner.

RICHARD M. WOOD, Examiner.

R. F. DROPKIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,350,772 November 7, 1967 John B. Ulam et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column Z, line 22, for "Thus" read This column 3, in the table, first column, line 4 thereof, for "304" read 302 line 40, after "aluminum" insert below its same line 40, for "temperatures" read temperature Signed and sealed this 7th day of January 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. A METHOD OF FORMING A COMPOSITE STAINLESS STEEL AND ALUMINUM METAL OF AT LEAST ONE STRIP OF EACH OF ALUMINUM AND STAINLESS STEEL COMPRISING THE STEPS OF HEATING THE STRIP OF STAINLESS STEEL ABOVE ITS STRESS RELIEVING TEMPERATURE BUT BELOW ITS FUSION TEMPERATURE WHILE MAINTAINING THE ALUMINUM STRESS RELIEVING TEMPERATURES, IMMEDIATELY BRINGING THE SURFACES OF THE HEATED STAINLESS STEEL AND THE ALUMINUM TOGETHER AND EXERTING PRESSURE ON THE METALS SIMULTANEOUSLY TO EFFECT REDUCTION AND TO FORM A BOND BETWEEN THEM.
 2. A METHOD OF FORMING A COMPOSITE STAINLESS STEEL AND ALUMINUM METAL OF AT LEAST ONE STRIP OFEACH OF ALUMINUM AND STAINLESS STEEL COMPRISING THE STEPS OF SEPARATELY AND DIFFERENTIALLY HEATING EACH OF THE STAINLESS STEEL AND ALUMINUM TO A TEMPERATURE ABOVE ITS OWN INDIVIDUAL RECRYSTALLIZATION TEMPERATURE BUT BELOW ITS FUSION POINT AND IMMEDIATELY BRINGING THE DIFFERENTIALLY HEATED STRIPS TOGETHER WHILE MAINTAINING A TEMPERATURE DIFFERENTIAL BETWEEN THEM PROPORTIONAL TO THE DIFFERENCE OF THEIR MINIMUM STRESS RELIEVING TEMPERATURES AND EXERTING PRESSURE ON THE METALS SIMULTANEOUSLY TO REDUCE AND BOND THEM. 